30 Jul Damage, disruption & downtime
Even the shortest period of downtime can damage the reputation of a data centre or enterprise, resulting in the loss of customer trust and subsequent business. Alan Elder, Fellow Engineer, Tyco Systems examines a research study on the impact of sound on computer hard disk drives and risk mitigation measures.
Data centres are relied upon to store and distribute valuable information for customers across many industries, from the investment banking to the healthcare sector.
This valuable information is primarily stored on Hard Disk Drives (HDDs). Industry demands that data centres remain functional 24 hours a day, 7 days a week, 365 days a year. The Middle East region is seeing substantial investment in new data centre infrastructure to support the growth in mobile telecommunications, cloud computing and combined internet/web application usage.
According to recent research, the proportion of outsourced (cloud) data centre capacity in the UAE and Gulf states has seen considerable growth, increasing from 11.8 percent in 2014 to 13.7 percent by 2020. Providing adequate protection for this vital infrastructure is key to operational uptime and business continuity. However, there are a myriad of factors that can affect the viability of a data centre, and not only potential hazards that can lead to physical damage and asset loss.
Protecting the connected world
One way of reducing the risk of downtime or lost operation time is to minimise the impact of fire. These events have a significant effect on the operational viability of a data centre, and threaten the safety and security of its assets. Protecting against fire damage is a critical consideration when designing and operating a data centre to ensure maximum uptime and avoid unnecessary disruption and cost to recover from a fire event. Installing an inert gas fire suppression system is one option to provide effective protection for data centres. Yet understanding the application requirements is key.
These systems have shown, through discharges in the field, that HDD performance may be reduced or permanent damage may occur to this sensitive electronic equipment, as a result of exposure to high acoustic levels. To gain a greater understanding of the impact of acoustic energy on hard drives, Tyco Fire Protection Products (Tyco), in collaboration with Michigan Technological University (MTU), conducted a holistic study of HDD performance with respect to acoustic energy, room acoustics, and suppression system nozzle acoustics.
The sound output of fire suppression systems is dependent on many factors. These include discharge duration, peak agent flow rate, valve technology, and many others. Extensive research and modelling of inert gas agent flow was performed to develop an inert gas suppression nozzle generating a low sound output, expressed as the Sound Power Level.
The research conducted by Tyco and MTU focused on the fact that every hazard area protected by a fire suppression system will yield varying sound path absorption properties. Data centres should perform room acoustic calculations to ensure the fire suppression system installation will meet the sound performance requirements to help reduce the risk of HDD degradation should the system discharge. The sound pressure level (SPL) calculation method requires the use of advanced acoustic formulas to determine the sound absorption between the fire suppression system nozzles and the data centre HDDs.
Research test methodology
An experimental test set-up designed to quantify the read/write performance reduction of HDDs when exposed to noise across frequency bands and at varying sound pressure levels. The test set-up employed a data acquisition system to control the testing process, record the SPL in one-third octave (OTO) bands and evaluate the HDD read/write speeds. The test used a sample of 12 enterprise model HDDs to represent the commonly found equipment in today’s data centres. The 12 HDDs contained samples from five different brands, with capacities ranging from 320 gigabytes to 10 terabytes.
The HDDs were placed in a soundproof chamber to avoid unwanted path effects, such as reflections, or spurious external noise sources. The testing setup ensured precise control of the SPL at the surface of the HDD by utilising a real-time control system capable of dynamically adjusting the input signal to the noise source. This SPL control was achieved by means of a feedback loop in the data acquisition system. The feedback control system consisted of a power amplifier, compression drivers, an electrical current probe and a surface-mount microphone located on the top surface of the HDD. The data acquisition system used the real-time SPL reading at the HDD to adjust the noise output of the compression drivers and ensure a constant noise application during each test. The unweighted SPLs were measured in one-third octave (OTO) bands.
HDD performance during the acoustic testing was captured by monitoring the drive read/write speeds. The read/write performance was conducted using a random process of different sized data packets. The block sizes of the data packets varied from 10 KB to 8 MB. The write test was performed first followed by the read test for all experiments.
Baseline read/write speed tests, with no sound source present, was captured for each HDD to establish the normalised 100% drive performance level. Once the baseline was established, the HDDs were then subjected to acoustic sensitivity testing. Several baseline tests were conducted throughout the evaluation of each HDD to ensure no permanent damage had been induced by the testing.
Driving new product development
Examining the research results, Tyco used this insight to develop a new inert gas suppression nozzle generating a low sound power level. This nozzle is an innovative advancement in nozzle technology for the data centre market, providing an effective solution to reducing sound exposure to sensitive HDDs. The development culminated in area coverage testing that resulted in extensive coverage areas from the standard acoustic nozzle, which will allow the number of nozzles to be reduced and potentially reduce the piping requirements. With this opportunity to reduce piping, the average installation cost may be lower when compared to other acoustic solutions available.
The sound absorbing materials within the nozzle were selected based on the extensive research and physical acoustic testing. The nozzle was rigorously tested through hundreds of suppression system discharges, resulting in superior sound power performance and suppression capabilities rivalling standard suppression nozzles. The area coverage and flow capabilities, as tested with Tyco’s Inert Gas fire suppression system hardware, in line with ANSI UL 2127 nozzle tests have resulted in the following performance:
• Maximum protected height per nozzle: 6.1m
• Area coverage: 9.8m x 9.8m
• Agent flow rate capabilities: up to 142 m3/min (5000 cfm)
The acoustic research study also supported the development of a novel tool for performing acoustic calculations for data centres. An Acoustic Calculator helps to estimate the sound pressure level at a HDD location generated by an inert gas suppression system using the Acoustic Nozzle.
The Acoustic Calculator simplifies the calculation by containing drop down menus for the suppression system parameters, as well as a selection of room materials and the equipment within the data centre. This enables Tyco’s Technical Services team to perform calculations tailored to each customer installation.
In conclusion, this comprehensive research study has identified the noise sensitivity of enterprise HDDs, believed to be the largest range of equipment tested to date and as a result it is recommended that data centres specify sound pressure levels of 110 dBZ or below across 500Hz – 10KHz frequency bands at HDD locations.
Data centre owners and operators must also consider the sound-path-receiver paradigm and understand that sound is generated as sound power at a source and transformed through the room paths to generate the sound pressure at HDDs.
A continued commitment to creating solutions for the data centre market led to the development of Tyco’s new low sound power fire suppression nozzle that provides system designers and data centre owners and operators with tangible performance benefits, supported by extensive research, product development and testing.
To find out more about the findings of the acoustic research study, download the whitepaper at http://www.hygood.com/Literature/Sound-White-Paper-Data-Center-web.pdf.